They were scared of how rapidly it was spreading. It had taken control of some strong powers which the Americans feared could lead to a war. It lead to the cold war which isn't a physical war but it was a very frightening. Both sides had control over hundreds of nuclear warheads, so yea, we peed our pants. All it took was a simple remark to mark the end of humanity. It went a little like this;
Communist: Say I wont press the button.
Us: You wont.
Coms: WHAT??? *Reaches for button*
US: NO I WAS JOKING! WE WILL DO WHATEVER YOU WANT!
Coms: Keep talking...
And that pretty much what happened. The communist were strong back then, who knows what there capable of in the future.
Hope I helped. :)
Answer:
B. Imperial nations began moving further inland and governing colonial subjects.
